Exactly where the bridge is located (2,3,4)
I believe the answer is:
on the nose
I believe this clue is a double definition.
'exactly' is the first definition.
(I know that exactly can be written as on the nose)
'where the bridge is located' is the second definition.
(as in the bridge of a pair of glasses)
(Other definitions for on the nose that I've seen before include "where glasses are found?" , "just to take the first place" , "characteristic of glasses?" , "where glasses rest" , "where might a boxer's punch land?" .)